The present inventive concept herein relates to optical devices, and more particularly, to a photo detector and an optical device including the photo detector.
A photo detector is a device that is essentially used in an optical communication. The photo detector converts light into an electric signal. The photo detector requires high responsivity, a high operation speed, a high power capability, etc. Responsivity represents how many photocurrents are generated with respect to input optical signal and may correspond to receiving sensitivity. An operation speed is standards for processing large amounts of data. A power capability is one of important factors for realizing a long-distance communication. An optical amplifier is disposed at every certain distance to compensate loss being generated in a long-distance communication. At this time, a high power input may enter a photo detector. Thus, the photo detector has to smoothly operate with respect to the high power input.
A photo detector is being used in the field of photomixer. The photomixer has a similar function to a radio frequency mixer. For instance, if a radio frequency signal having frequencies f1 and f2 is input to the radio frequency mixer, the radio frequency mixer can generate radio a frequency component f1-f2 (where, f1>f2). Similarly, if a laser beam having different frequencies from each other is input to a photomixer, the photomixer can output an electric signal having a frequency component corresponding to a difference of the input frequencies. That is, the photomixer can generate a high speed electric signal of terahertz wave using a laser beam. Thus, the photomixer can have high responsivity, a high operation speed and a high power capability. The high responsivity is an important factor as standards for increasing an efficiency of converting a laser beam into an electric signal. When the photomixer has a high operation frequency, it can output a high speed electric signal of terahertz wave. Also, the photomixer can operate at high speed in proportion to an input power of optical signal. The photo detector and the photomixer for optical communication have different uses but same performance is required for the photo detector and the photomixer.